Unified Rotation Curve of the Galaxy -- Decomposition into de Vaucouleurs Bulge, Disk, Dark Halo, and the 9-kpc Rotation Dip --

TL;DR

This paper reconstructs a detailed rotation curve of the Milky Way, decomposes it into fundamental components, and identifies peculiar dips likely caused by rings or galactic structures, providing new insights into galactic mass distribution.

Contribution

It presents the first r^{1/4}-law fit for the Milky Way's rotation curve and models the galaxy with bulge, disk, and dark halo components, explaining the 9-kpc dip as a massive ring.

Findings

First r^{1/4}-law fit for Milky Way rotation curve

Identification of a prominent 9-kpc rotation dip

Proposed explanation of the dip as a massive ring

Abstract

We present a unified rotation curve of the Galaxy re-constructed from the existing data by re-calculating the distances and velocities for a set of galactic constants R_0=8 kpc and V_0=200 km/s. We decompose it into a bulge with de Vaucouleurs-law profile of half-mass scale radius 0.5 kpc and mass 1.8 x 10^{10}M_{sun}, an exponential disk of scale radius 3.5 kpc of 6.5 x 10^{10}M_{sun}, and an isothermal dark halo of terminal velocity 200 km/s. The r^{1/4}-law fit was obtained for the first time for the Milky Way's rotation curve. After fitting by these fundamental structures, two local minima, or the dips, of rotation velocity are prominent at radii 3 and 9 kpc. The 3-kpc dip is consistent with the observed bar. It is alternatively explained by a massive ring with the density maximum at radius 4 kpc. The 9-kpc dip is clearly exhibited as the most peculiar feature in the galactic rotation curve. We explain it by a massive ring of amplitude as large as 0.3 to 0.4 times the disk density with the density peak at radius 11 kpc. This great ring may be related to the Perseus arm, while no peculiar feature of HI-gas is associated.